Adding BlockMeanCalculator for AEC.

webrtc/modules/audio_processing/utility/mean_calculator.h

+/*
+ *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_MODULES_AUDIO_PROCESSING_UTILITY_MEAN_CALCULATOR_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_UTILITY_MEAN_CALCULATOR_H_
+
+#include <stddef.h>
+#include <vector>
+
+#include "webrtc/base/criticalsection.h"

[peah-webrtc, 2016/03/18 09:18:34]

criticalsection.h should be after before  constructormagic.h

[minyue-webrtc, 2016/03/21 15:27:51]

Done.

+#include "webrtc/base/constructormagic.h"
+#include "webrtc/base/optional.h"
+
+namespace webrtc {
+
+// MeanCalculator calculates the mean of a sample sequence of a certain length.

[peah-webrtc, 2016/03/18 09:18:34]

I think it is better if this class is about the mean of values rather than of
samples. It is actually used in the code for storing levels and not samples.
Please also change the name of the member variables according to the term you
choose.

[minyue-webrtc, 2016/03/21 15:27:51]

In statistics, sample has its own meaning, and should not be confused with
"audio sample". If you think it can still be confusing, I am fine with changing
it to "value".

+class MeanCalculator {

[peah-webrtc, 2016/03/18 09:18:34]

As I said in the previous review I think you should change the class name to
better reflect what it does.

+ public:
+  explicit MeanCalculator(size_t window_length);
+
+  // Reset.
+  void Reset();
+
+  // Add one sample to the sequence.
+  void AddSample(float sample);
+
+  // Return the number of newly added samples since latest update on mean value.
+  size_t GetNumberNewSamples() const;

[peah-webrtc, 2016/03/18 09:18:34]

What about GetNumberOfNewSamples()?

[minyue-webrtc, 2016/03/21 15:27:51]

Done.

+
+  // Return the latest mean value.
+  float GetLatestMean() const;
+
+ private:
+  // Clear all samples added.
+  void Clear();
+
+  // Update |sum_| and |compensation_| using Kahan algorithm.
+  void KahanSum(float sample);
+
+  const size_t window_length_;
+  size_t count_;
+  float sum_;
+  float compensation_;
+  float mean_;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(MeanCalculator);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_UTILITY_MEAN_CALCULATOR_H_